For an OFDMA wireless system supporting hybrid communication of data and voice, a narrowband user and a broadband user may access the wireless system simultaneously. Therefore, there is a need to plan a sub-carrier flexibly to adapt to service traffic variation in real time. On the other hand, a narrowband service has much higher requirements for signal reception quality. Particularly, factors such as frequency and time selectivity of a mobile channel, frequency and time selectivity of co-frequency interference, inter-symbol and inter-carrier interference resulted from serious multi-path, interference resulted from circuit nonlinearity and phase noise may all lead to a significant decrease in the signal reception quality.